* Coal is formed from the accumulation and compression of plant matter, primarily trees and ferns, over millions of years. The organic material decomposes under anaerobic conditions (without oxygen) and undergoes a series of chemical transformations, eventually forming coal.
* Limestone is primarily formed from the accumulation of the skeletal remains of marine organisms, such as corals, mollusks, and algae. These organisms contain calcium carbonate (CaCO3), which forms the main component of limestone.
Therefore, both coal and limestone are classified as biogenic sedimentary rocks, meaning they are formed from the remains of living organisms. They are not formed from inorganic processes like igneous or metamorphic rocks.
While some people might refer to them as biological rocks, it's more accurate to call them biogenic sedimentary rocks to emphasize their origin from living organisms and their sedimentary nature.
